1. Field of the Invention
The present invention relates to shielding assemblies and, more particularly, an improved shielding assembly that can be used with an intrusion detection system employing microwave radar.
2. Description of the Related Art
A variety of devices generate electrical and magnetic fields that may require shielding to prevent undesired emissions. One example of such a device are intrusion detection systems that employ microwave radar. Such systems generate microwave pulses at a predetermined frequency to detect objects and the motion of such objects. Microwave radar systems also typically generate unwanted radio frequency (RF) emissions at other frequencies. Intrusion detection systems employing microwave radar are generally subject to governmental regulations, e.g., by the FCC in the U.S. and by the CE in the European Union, that place limits on such unwanted RF emissions.
To attenuate the unwanted RF emissions, it is known to use a metallic box-like enclosure to enclose the electronic circuitry generating the unwanted RF emissions or to place the entire circuit inside a sealed metallic enclosure. Conducting elements entering and exiting the enclosure may also be filtered to reduce RF emissions. Although such metallic enclosures perform well in preventing the external emission of the unwanted RF energy, the metallic enclosures typically reflect, instead of absorb, much of the RF energy. The reflected RF energy can disrupt the circuits contained within the enclosure, generate noise within the system, and interfere with the filtering of the conducting elements entering and exiting the enclosure. It is also known to add foam or rubber sheets containing ferrite, carbon or metal powders to the interior of the enclosure walls to absorb some of the RF energy. These sheet materials, which may have military applications and be regulated by the government, are typically quite expensive. Consequently, a need exists for an alternative shielding assembly.